There have been several approaches to creating displays for "immersive viewing" (that is, where the user is completely surrounded by visual imagery created by electronic or other means), especially those supporting virtual reality environments. In these applications, the idea is to provide a viewing device, usually in the form of a head-mounted, or face mounted display system worn like a pair of goggles, that will produce an image which is viewable at close distances from each eye, and where the image produced appears to be large and at virtual infinity so that the eyes can focus on it.
Almost all attempts at virtual reality displays have used a planar display of some kind (usually a flat-panel liquid crystal display) and a lens system. FIG. 1 illustrates such a system 100. A housing 102 contains at one end a Liquid Crystal Spatial Light Modulator (LC SLM) 104 and a diffuse backlight 105. At the other end is an aperture 106 through which a user's eye 108 may look into the system. Interposed between the aperture 106 and the LC SLM 104 is bulk optics 110 (represented in FIG. 1 by a double convex lens element) for focusing the LC SLM 104 image onto the eye. Note that in order for the image from the SLM to focus properly on the user's eye 108, there is a first length 112, which is substantially a first focal length of lens 110 between the LC SLM 104 and the optics 110, and a second length 114, which is substantially a second focal length between the optics 110 and the aperture 106. There are many variations on this structure, but each attempts to portray a magnified image for each of the user's eyes that appears to be placed at, or near, virtual infinity so that the eye can easily focus on it.
The resulting head-mounted displays are physically large due to (1) thick, low f-number, display-sized lenses used in lens system 110 and (2) the long optical path lengths required for these lenses. The displays are also heavy, due to the weight of the glass or plastic comprising the optics, and uncomfortable to wear because this large and heavy display/lens-system is cantilevered out over the front of the head and tends to tilt the wearer's head forward.
In more advanced head-mounted displays (e.g., those used in military aircrafts), the image is often relayed by a series of mirrors and/or intermediate lenses, or even coherent bundles of optical fiber, from a display that is remote from the eye. In these cases, one or more bulk lenses (or mirrors) are again used at the end of the optical relay system closest to the user's eye to create an image that appears to be at virtual infinity. Some displays use a semi-transparent visor as part of the virtual imaging system and cause the ultimate virtual image to be displayed by way of partial reflection. Again, focal lengths on the order of several inches and large reflecting surfaces make these systems cumbersome and bulky.
Techniques such as described in Hildebrandt, et. al., Apr. 29, 1997, U.S. Pat. No. 5,625,372, attempt to decrease the overall size of the device while still using bulk optics by using a folded optical path. These techniques, however, are unlikely to be able to produce a truly planar device since they still employ bulk optics with focal lengths measured as a large fraction of the diameter of the optics.
The size of these prior art display systems also rules out their use in applications requiring small or flat displays such as in SmartCards.
Reflection Technology Inc., of Waltham, Mass., provides a head-mounted display called "Private Eye". This head mounted display uses a linear array of LEDs to create the image. The image of the LEDs is swept back and forth through a fixed angle by a vibrating mirror. The swept image is viewed through one or more bulk optics lenses. (This technology is used, for example, in Sega's "Virtual Boy" product). Although the technique eliminates the 2-dimensional Spatial Light Modulator, it still uses bulk optics and results in a display that protrudes from the face much more than an ordinary pair of spectacles, and its non-planarity rules it out for use in places where flat virtual imaging displays are needed.
A head-mounted display developed at the University of Washington at Seattle, uses a laser beam to scan directly into the eye and "paint" an image on the retina. This technique could lead to a less bulky display, but requires a rather sophisticated scanning system and multi-colored lasers for a color image and in any event would not result in a planar display. This device is difficult and expensive to implement.
More recently, techniques such as that described in my U.S. patent application Ser. No. 08/767,751, filed Dec. 17, 1996, now U.S. Pat. No. 5,883,606, issued Mar. 16, 1999, provide a planar display by using microlens arrays and an array of apertures to mask each pixel of a liquid crystal (or other Spatial Light Modulator) such that light from each pixel is directly imaged on the retina thus forming a visible image at virtual infinity.
A drawback with this technique is the relatively fine manufacturing techniques required to create microlens arrays and aperture plates wherein each microlens is precisely aligned with a pixel and aperture plate element.
The purpose of this invention is to overcome the problems of the prior art, and specifically to create a family of displays that are:
Essentially planar, or which have thinner cross-section than other available virtual displays; PA1 Simple and low-cost to manufacture since in at least one embodiment there are no lenses or other traditional active optical element and each pinpoint light source (depending on simple design tradeoffs) can illuminate several tens, hundreds, or even thousands of pixels; and PA1 Can be made extremely bright since the pinpoints of light can be delivered from the sheared ends of optical fibers carrying as much light as required, with this light coming, for instance, from a small incandescent light bulb.